The present invention relates generally to electrical power distribution systems and more particularly to a specific system for and method of controlling the supply of electrical power to a plurality of outlets located at selected locations in the walls and ceilings of a building structure from control stations disposed at remote locations in the walls of the building structure.
Today, an electrical power distribution system typically found in a building structure utilizes copper wiring of sufficient size to connect the various electrical outlets within the structure to a central source of power. Generally, building codes require that this wiring be protected by enclosing it in metal conduit. Any particular outlet which is to be remote controlled, for example from a wall mounted switch, requires that the same copper wiring and conduit must be run to the wall plate. This switch is typically a mechanical device which opens and closes contacts to control the flow of current from the power source to the outlets.
There are a number of deficiencies with an electrical power distribution system of the type just described. For example, this type of system is quite inflexible. Wiring connections are permanent and impractical to change after construction. While it would often be desirable to change connections, for example, when furniture is moved or when a particular room is remodeled, or put to some different use, this is seldom practical since it involves pulling wires out of their associated conduits and inserting new wires, and often cutting into walls or floors to install new conduit.
In addition to this inconvenience and inflexibility, the extra wiring required to carry power to and through the various switching stations in a system of the type described above adds substantial cost to the overall installation, as much as 30 to 50 percent in a typical dwelling. Moreover, there is a certain element of danger in having the full power voltage close to the operator. In addition, these mechanical switches are subject to wear and tear; and the power supplied through the switches, typically 110 volt AC power at 60 Hz frequency, when applied or cut off by the switches at random times, results in harsh treatment to some appliances. For example, if contact closure occurs at the peak value of the voltage, a cold lamp filament receives a severe excess of current and may burn out just as the switch is closed.
The various deficiencies just recited, along with others have led to distribution systems which do not route the power wiring to the wall mounted switches. These systems utilize signalling devices at the remote control stations for sending messages to the various outlets over circuits which are separate from the power wiring. Power switching may be accomplished at these outlets or at a central location where several outlets are controlled by means of electromechanical relays. Another method which has been suggested is to send a coded sequence of pulses (or specific frequencies) to electronic circuits at the various outlets.
As will be seen hereinafter, the present invention relates to an electrical power distribution system of this latter type. In this regard, applicant has found there to be a similarity between the control functions required in a system of this type for use in a building structure and the control functions employed in modern computers and communication systems. More specifically, the computers and communications systems of today include highly developed functions including digital coding of messages, multiplex signaling, that is, sending several messages over a single line, and the use of solid state integrated circuitry for reliable and inexpensive signal processing. As will be seen hereinafter, applicant has found a way to apply this technology to electrical power distribution systems with the result being superior performance and reduced cost.
In a computer, a great deal of information is circulated among the various components. Typically, this information is coded in binary form. Also, there is generally a definite format for allowable messages. For example, each message may consist of a fixed number of pulses which are either present or absent and which run in sequence at a fixed rate, specifically at a "clock" frequency. A suitable oscillator may generate this "clock" frequency or "clock" signal as it is called and all parts of the computer are kept in synchronism by receiving this signal. Both data and instructions for processing such data circulate on buses, which are conductors interconnecting several sections of the computer. A great many messages can travel on a single bus provided they occur at different times. Messages, such as for example the closure of a certain key on a keyboard, are turned into suitable sequences of pulses by encoders. A typical encoder is an electronic circuit which generates a characteristic string of pulses when actuated by a suitable input. Coded messages are made effective at the receiving end by decoders. A typical decoder is an electronic circuit capable of responding to a particular sequence of pulses, that is, to a particular message, causing the decoder to produce an output signal, for example a change of voltage at its output. This signal indicates that the particular message has been received. A great many other messages from other encoders might flow over the same bus without any effect on the specific decoder, which responds only to one specific message. As will be seen hereinafter, applicant has found these various techniques useful for providing an economical and yet reliable electrical power distribution system for controlling the supply of electrical power to a plurality of outlets located at selected locations in the walls and ceilings of a building structure.